The present invention relates to a system for separating fluids. More particularly, the invention relates to a system for separating fluids of different densities. The invention is primarily, but not exclusively, directed to a system for separating oil from water and sediment to reclaim and recycle used oil.
The present invention makes use of the fact that a mixture of two liquids of different densities will have a tendency to separate; the heavier liquid will sink and the lighter liquid will rise above the heavier liquid. The amount of separation of the two liquids depends, in part, on the differences in their densities. The greater the differences in density, the more clearly defined will be the separation between the liquids.
The present invention is particularly suited to the separation of oil and water for reclamation purposes. During the various stages of processing, transporting and storing oil, impurities, primarily including water but also including metals, dirt, etc., tend to mix with the oil. Mixing occurs to a greater or lesser degree depending on such factors as the density of the oil, temperature of the mixture, amount of agitation (e.g., due to wave action) to which the mixture is subjected, and rates of flow through a pipeline.
State-of-art methods for separating oil and water mixtures depend on the difference in the densities of the water and oil or other suspended matter present to effect physical separation. The primary processing techniques available are settling (i.e., gravity separation), centrifugation, demulsification (with heat and/or chemicals), and distillation.
Settling is the simplest technique that can be applied to the separation of water from oily waste mixtures. The effectiveness of the settling technique for separating oil-water mixtures depends on the amount of oil contaminant present as globules and the size of these globules. Gravity separation will not remove oil dissolved in water. Though inherently simple, the gravity separation technique is also basically slow and very long residence times may be required to remove small globules of oil.
Centrifugation utilizes the centrifugal force developed by rapid rotation of a system to enhance the settling rates of oil globules and solid matter suspended in water. Oil-water separation by centrifugation is only practical when the oil and/or solids contaminants are present in relatively high concentrations. Centrifugation is also generally ineffective in removing highly stabilized emulsions of oil in water (though some emulsions may be broken by centrifugation) or oil dissolved in water. Its application to the processing of oily wastes depends on the specific nature of the wastes concerned, their concentration, variability, etc.
The breaking of stable oil-water emulsions can be an important primary processing step in the treatment of some oily wastes. In the presence of stabilizing chemical dispersants such as used in bilge cleaners, simple settling or even centrifugation may not be able to effect oil-water separation. Under these conditions, other special physical or chemical processing techniques can be used.
The less stable emulsions can often be broken by physical techniques such as heating. This is the simplest and least expensive approach. Heating reduces oil viscosity, melts waxy interfacial films and promotes coalescence and separation of the oil and water phases. Simultaneous application of heat and centrifugation (or filtration) may be required to separate emulsions of comparatively high stability.
Very stable emulsions (which fail to yield to physical methods alone) must be treated chemically to aid the physical processes. Chemical demulsifiers work primarily by the neutralization of stabilizing electrical charges and alteration of the system hydrophyllic/lipophillic balance (HLB). There are many chemical demulsifiers on the market. The selection of which type of chemical demulsifier to use will depend on the specific character of the emulsion to be treated and the nature of the active stabilizing agents present.
Most oily wastes (on the order of 90%) can be satisfactorily treated using one or more processes involving gravity separation, heat, and centrifugation. Chemicals are generally used only where needed and other techniques are not sufficient.
Gravity separation, heat, and centrifugation can produce oil having a BS&W (bottoms, sediment, and water) of less than 0.1%. Overall, therefore a process involving gravity, heat, and centrifugation will produce oil of the highest quality and the least amount of oily sludge. The other processes will produce oil having lower overall quality and higher sludge levels. The process most effective in breaking emulsions will probably produce the least amount of oily sludge, since oily sludge is no more than a highly stable emulsion containing a fairly high solids content.
Oil separated out of the residue mixture or the drawn off water and containing 2% or less of residue BS&W can be recycled and returned to the commercial product stream. Prior art separation techniques are generally time consuming (in the case of settling tanks), or expensive (due to cost of the centrifuges, chemicals, and related equipment), or have other problems which make them commercially impractical or expensive.
The present invention provides a cost effective way to separate oil out of oil/water residue and to reclaim oil having as little as 0.5% or less BS&W. The invention provides a relatively high rate and degree of separation without the expensive or moving parts of a mechanical centrifuge. Also, the present invention is less likely to become clogged with trash than mechanical centrifuges.